AZIMUTHAL STRUCTURES IN THE WIND AND CHROMOSPHERE OF THE HERBIG-AE STAR AB-AUR - PRELIMINARY-RESULTS FROM THE MUSICOS 1992 CAMPAIGN

MUSICOS (for MUlti-SIte COntinuous Spectroscopy) is an international p roject to facilitate and organize world-wide multi-site campaigns in h igh resolution spectroscopy, in view of obtaining a complete time cove rage of various types of variable stellar phenomena. In the framework of this project a vast spectroscopic campaign was organized in Decembe r 1992, involving 8 sites well distributed in longitude around the Ear th. The observations concerned three scientific programs, among which was the study of azimuthal structures in the wind and chromosphere of the pre-Main-Sequence Herbig Ae star AB Aur. The HeI 5876 Angstrom lin e of AB Aur, which is formed in the expanding chromosphere of this sta r, in the innermost parts of its wind, was monitored at a resolution o f 30000, nearly continuously for about 4 days. A spectacular variabili ty of this line was discovered, the profile changing from pure emissio n to a composite profile including a deep absorption component in the course of a few hours. This variability can be the signature of azimut hal structures in the wind of AB Aur. We present the data collected du ring the campaign, and discuss possible interpretations of the spectac ular variations of the He I 5876 Angstrom line.